Modern medicine uses many diagnostic procedures where electrical signals or currents are received from a mammalian patient's body. Nonlimiting examples of diagnostic procedures include electrocardiographic (ECG or EKG) diagnosis or monitoring of electrical wave patterns of a mammalian heart, irrespective of duration or circumstance. The point of contact between medical equipment used in these procedures and the skin of the patient is usually some sort of biomedical electrode. Such an electrode typically includes a conductor which must be connected electrically to the equipment, and an ionically conductive medium adhered to or otherwise contacting skin of a patient.
Among diagnostic procedures using biomedical electrodes are monitors of electrical output from body functions, such as electrocardiographs (ECG) for monitoring heart activity and for diagnosing heart abnormalities.
For each diagnostic procedure, at least one biomedical electrode having an ionically-conductive medium containing an electrolyte is adhered to or otherwise contacting skin at a location of interest and also electrically connected to electrical diagnostic equipment. A critical component of the biomedical electrode is the electrical conductor in electrical communication with the ionically-conductive medium and the electrical diagnostic equipment.
Electrical conductors require excellent electrical conductivity and minimal electrical resistance for biomedical electrodes, especially when faint electrical signals are received from the patient. For this reason, metals or carbon (especially graphite) are used. Among metals, silver is preferred because of its optimal conductivity. But biomedical electrodes which monitor a patient's conditions must have a stable half cell potential and be able to withstand the polarizing effects of a defibrillation procedure for a heart. For this reason, a metal halide, such as silver chloride, is preferably used with a metal conductor, such as silver, to create a depolarizable electrical conductor in biomedical electrodes which can monitor a heart.
One principal difficulty with a biomedical electrode containing silver/silver chloride is the expense of silver.
Others have attempted to reduce the cost of silver in biomedical electrodes by using graphite or other galvanically inactive materials in association with silver particles or silver/silver chloride layers. See, for example, U.S. Pat. Nos. 3,976,055 (Monter et al.) and 4,852,571 (Gadsby et al.).
Others have used other galvanically inactive electrical conductors in biomedical electrodes. See, for example, U.S. Pat. Nos. 4,846,185 (Carim), which discloses ferrous/ferric chloride and galvanically inactive metals and PCT Patent Publication No. WO 95/20350 (Takaki), which discloses galvanically inactive inorganic oxides in a galvanically inactive binder.
Others have combined the purposes of biomedical electrodes to accomplish both diagnosis/monitoring of bioelectric signals with delivery of therapeutic electrical signals into the body of a patient. See, for example, U.S. Pat. Nos. 4,419,998; 4,494,552; 4,834,103; 4,848,103; 4,848,345; 4,850,356; 4,852,585; and 4,895,169 (all Heath); and PCT Publication WO 94/26950 (Robbins et al) for the use of a single electrode to both monitor bioelectric signals from the body and delivery pacing or defibrillation electrical signals to the body of a patient in need.
Others have provided multiple electrical conductors on a single biomedical electrode for a variety of purposes. See, for example, U.S. Pat. Nos. 2,536,271 (Fransen); 3,720,209 (Bolduc); 4,381,789 (Naser et al.); 4,807,621 and 4,873,974 (both Hagen et al.) for the delivery or return of high frequency energy; 5,295,482 (Clare et al.) for the creation of differing resistances on a dispersive electrode plate for electrosurgery; and PCT Publication No. WO 94/27491 (Burgio et al.) for the placement of two transcutaneous electrical nerve stimulation (TENS) electrodes on a common carrier for compact delivery of therapeutic electrical signals for intraoral procedures.
In each instance, the biomedical electrode has employed a field of conductive hydrogel or adhesive to contact or adhere to mammalian skin and to receive the electrical signals and transmit them ionically to an electrical conductor for electrical connection to biomedical instrumentation.
Representative examples of biomedical electrodes include U.S. Pat. Nos. 4,352,359 (Larimore); 4,524,087 (Engel); 4,539,996 (Engel); 4,554,924 (Engel); 4,848,348 (Carim); 4,848,353 (Engel); 5,012,810 (Strand et al.); 5,133,356 (Bryan et al.); 5,215,087 (Anderson et al.); and 5,296,079 (Duan et al.).
Biomedical electrode construction has increasingly employed a tab/pad style of construction. A number of biomedical electrode constructions have employed an insulative outer layer through which an electrically conductive tab extends to provide a low profile, multi-layer construction. Representative examples of such constructions are disclosed in the embodiments shown in U.S. Pat. No. 5,012,810 (Strand et al.).
Another low profile multi-layer construction employs an electrically conductive tab which remains below the surface of the outermost layer but is accessible to the outside through an aperture in the outermost layer. A representative example of this electrode construction is disclosed in U.S. Pat. No. 5,215,087 (Anderson et al.).
Other biomedical electrode constructions involve an elaborate placement of sponges in apertures to which an electrically conductive tab can contact even though that tab does not extend beneath the surface of the outer most layer. Representative examples of this construction is found in U.S. Pat. No. 3,977,392 (Manley), U.S. Pat. No. 4,522,211 (Bare et al.) and U.S. Pat. No. 4,838,273 (Cartmell).
Another biomedical electrode construction employs a reservoir of conductive gel into which a lead wire can be inserted through an aperture, as disclosed in U.S. Pat. No. 4,409,981 (Lundberg). Another biomedical electrode construction employs an aperture in communication with a conductive adhesive into which a lead wire can be inserted through the aperture, as disclosed in U.S. Pat. No. 4,715,382 (Strand).
Because biomedical electrodes are disposable and are generally disposed after a single use, cost/benefit analysis of biomedical electrode usage is continuously under health care cost scrutiny. The more that a single biomedical electrode can provide for the least amount of cost is a goal of both manufacturers and the consumers they serve.
For example, about 10 diagnostic biomedical electrodes are required for each electrocardiogram (ECG) procedure. Such diagnostic biomedical electrodes are presently designed for a single purpose and for a single use, making the cost of such electrodes to customers very sensitive to manufacturing techniques and performance features. Unfortunately in some diagnostic electrodes, the cost of manufacture outweighs the performance properties of the electrode.
The same cost/benefit analysis issues arise with more expensive biomedical electrodes that are used less frequently but are designed for one or more than one performance purpose.